Spontaneous polarization-induced nanohelixes, nanosprings, and nanorings of piezoelectric nanobelts

Growth of (0001) facet-dominated, free-standing, piezoelectric zinc oxide (ZnO) nanostructures is challenged by the divergence of the surface energy due to intrinsic polarization. By controlling growth kinetics, we show the success of growing nanobelt-based novel structures whose surfaces are dominated by the polarized +/- (0001) facets. Owing to the positive and negative ionic charges on the zinc- and oxygen-terminated +/- (0001) surfaces, respectively, a spontaneous polarization is induced across the nanobelt thickness. As a result, right-handed helical nanostructures and nanorings are formed by rolling up single-crystal nanobelts; this phenomenon is attributed to a consequence of minimizing the total energy contributed by spontaneous polarization and elasticity. The polar-surface-dominated ZnO nanobelts are likely to be an ideal system for understanding piezoelectricity and polarization-induced ferroelectricity at nanoscale; and they could have applications as one-dimensional nanoscale sensors, transducers, and resonators.